Webb Office Hours Session 11: July 11, 2024
Q&A's:
Q1: Where are the Webb Office Hours procedures and guidelines?
A1: Webb Office Hours. Type your question into the WebEx chat. We will asynchronously copy questions from the chat to this main page and work through them as a group. If you have images to share please give WebEx permission to share your screen (you may need to log out and log back in again to enable this feature.)
Q2: What is the accuracy of NIRSpec IFU wavelengths? Using gratings G395H and G235H. Needed to calculated uncertainties in measured velocities. Is the accuracy published.
A2: Typical accuracy for those gratings is 15 km/s. There is evidence of a field dependence with degraded wavelength accuracy. Please file a Help Desk ticket with your example, so we can investigate further.
Q3: Is it possible to get some quasars from the MAST archive? Interested in the redshift and distance.
A3: The JWST archive provides images and spectra, but not measured quantities like redshift. High-level science products could have measured quantities, but there are no redshifts currently. There is a list of high level science products maintained here. Abstracts for approved programs are available here, which can provide a starting point to use in the MAST search form. This link provides information about how to use the Missions MAST interface.
Q4: Which pipeline version will fix the warm pixel issue in NIRSpec IFU and MIRI MRS? Will astrometric accuracy be improved as well? See an offset of ~0.2 arcsec.
A4: Use the 1.15.1 version. Still being tested, but worth trying now. Contains a number of improvements to NIRSpec IRS2 IFU cosmic ray flagging. No astrometric updates in the latest releases. Offset is typical of spacecraft pointing uncertainty.
Q5: Two different versions of the pipeline are yielding different results. What is going on? How should I proceed? Help Desk ticket already filed.
A5: Mostly likely explanation is that LaCosmic is flagging too many pixels as bad pixels, causing the dropouts in the data. Generally the MRS calwebb_spec3 outlier detection should be sufficient to reject such bad pixel artifacts though. Another possibility to try is the new self-calibrated bad pixel mask step in the 1.15.1 pipeline- this is still in a very early form of implementation and tricky to use, but we can follow up on the ticket to explain how to try it.
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